Abridged map generating apparatus, on-vehicle information terminal, abridged map distribution system and abridged map generating method

ABSTRACT

This abridged map generating apparatus includes an abridged map generation unit that generates an abridged map in which a shape of a road is simplified based upon road map data, wherein the road map data specifies the shapes of the road by shapes of links set for each predetermined road section, and the abridged map generation unit generates the abridged map by simplifying a shapes of a link or link series with fixed positions of both end points of the link or link series made by lining up a plurality of the links.

INCORPORATION BY REFERENCE

The disclosure of the following base priority application is herebyincorporated herein by reference: Japanese Patent Application No.2004-302958 (filed upon 18 Oct. 2004).

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates to an apparatus which generates anabridged map produced by simplifying a road map.

2. Description of Related Art

There is a known method for simplifying the shape of a road based uponmap data for displaying a map. For example, with the apparatus disclosedin Japanese Patent laid-open application Publication No. 11-202762, theshape of the road is simplified by performing procedures such asstraightening or orthogonalization or the like upon the links whichspecify the road shape in the map data, and by displaying only landmarkinformation within a range which is regulated by a mask. An easilyviewed map is provided by displaying a map using the road shape whichhas been simplified in this manner.

However, with the apparatus disclosed in Japanese Patent laid-openapplication Publication No. 11-202762, the road shape is simplified byperforming procedures such as straightening or orthogonalization or thelike upon each of the links. When, among these, an orthogonalizationprocedure is performed, an influence comes to be exerted upon thepositions of the adjacent links, since the positions of the end pointsof the links undesirably shift. Accordingly it sometimes happens that,when simplifying a road shape which extends over a long distance, theposition of the road deviates greatly from its original position.

SUMMARY OF THE INVENTION

The abridged map generating apparatus according to the present inventionincludes an abridged map generation unit that generates an abridged mapin which a shape of a road is simplified based upon road map data,wherein the road map data specifies the shape of the road by shapes oflinks set for each predetermined road section, and the abridged mapgeneration unit generates the abridged map by simplifying a shape of alink or link series with fixed positions of both end points of the linkor link series made by lining up a plurality of the links.

In the above described abridged map generating apparatus, it isdesirable that when the abridged map generation unit simplifies theshape of the link or link series, any point set in advance upon the linkis selected as a preserved point and a position of the preserved pointand the positions of both the end points are fixed respectively.

Furthermore, in the above described abridged map generating apparatus,it is desirable that the abridged map generation unit selects a point asthe preserved point which is furthest from a first line segment whichconnects between both the end points among points set in advance uponthe link.

In the abridged map generating apparatus described above, there may beincluded a point selection unit that selects some point set in advanceupon, the link, a line segment setting unit that sets a plurality ofsecond line segments which connect between the point selected by thepoint selection unit and each of both the end points in order, adirection revision unit that revises the directions of each of thesecond line segments set by the line segment setting unit, so that eachangle which is formed between each of the second line segments and apredetermined direction set in advance becomes an integer multiple of anunit angle set in advance, an intersection point detection unit thatobtains a point of intersection on which respective prolonged linesegments obtained by prolonging the second line segments of which thedirection has been revised by the direction revision unit areintersected each other, a length revision unit that revises a length ofeach of the second line segments, so as to connect together the point ofintersection obtained by the intersection point detection unit and oneof the end points or one of the points selected by the point selectionunit, and wherein the abridged map generation unit generates theabridged map by simplifying the shape of the link or link series, byusing each of the second line segments of which the length are revisedby the length revision unit.

In the above described abridged map generating apparatus, it isdesirable that the point selection unit selects the point which isfurthest from a first line segment which connects between both the endpoints among points set in advance upon the link.

Furthermore, in the above described abridged map generating apparatus,it is desirable that the point selection unit further selects pointswhich are furthest from third line segments which connect between boththe end points and the selected point respectively among points set inadvance upon the link.

The on-vehicle information terminal according to the present inventionincludes the abridged map generating apparatus described above, and adisplay control unit that causes an abridged map generated by theabridged map generating apparatus to be displayed upon a displaymonitor.

The abridged map distribution system of the present invention includesthe abridged map generating apparatus described above, a distributionapparatus that distributes an abridged map generated by the abridged mapgenerating apparatus, a navigation apparatus that receives the abridgedmap distributed by the distribution apparatus.

The abridged map generating method according to the present inventionfor generating an abridged map in which road shapes have beensimplified, the method includes simplifying a shape of a link or linkseries while fixing positions of both end points of the link or the linkseries made by lining up a plurality of links based upon road map datawhich specifies the shapes of roads by the shapes of links which are setfor each predetermined road section.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a block diagram showing the structure of a navigationapparatus according to an embodiment of the present invention.

FIG. 2 is a flow chart of a procedure which is executed when searchingfor a plurality of routes to a destination which has been set, anddisplaying an abridged map of these routes.

FIG. 3A is a figure showing the map before abridgement.

FIG. 3B is a figure showing the map after abridgement.

FIGS. 4A, 4B, 4C, and 4D are figures for explaining the details of adirection quantization procedure for a case of division into twosections, which is utilized when generating an abridged map.

FIGS. 5A, 5B, 5C, and 5D are figures for explaining the details of adirection quantization procedure for a case of division into foursections.

FIGS. 6A, 6B, and 6C are figures for explaining a method for simplifyingthe read shapes of the routes by approximating each link shape with acurve.

FIG. 7 is a figure showing a situation in which the present invention isapplied to a communicating navigation system.

FIG. 8 is a figure showing a situation in which the present invention isapplied to a personal computer.

DETAILED DESCRIPTION OF PREFERRED EMBODIMENTS

The structure of the navigation apparatus according to an embodiment ofthe present invention is shown in FIG. 1. This navigation apparatus ismounted to a vehicle, and it searches out a plurality of routes to adestination which has been set, and generates and displays a map whichhas been abridged from a normal map (hereinafter termed an abridged map)by, for the entirety of each route, simplifying the road shapes and thelike based upon the normal map. And one among the plurality of routeswhich have been displayed is selected by the user, and the vehicle isguided to the destination by taking this route as the recommended route.The navigation apparatus shown in FIG. 1 comprises a control circuit 11,a ROM 12, a RAM 13, a current position detection device 14, an imagememory 15, a display monitor 16, an input device 17, and a disk drive18. A DVD-ROM 19 upon which map data is recorded is loaded in the diskdrive 18.

The control circuit 11 consists of a micro processor and its peripheralcircuitry, and, using the RAM 13 as a work area, performs various typesof procedures and control by executing a control program which is storedin the ROM 12. By procedures which will be explained hereinafter beingexecuted by this control circuit 11, a plurality of routes to adestination which has been set are searched out based upon the map datarecorded in the DVD-ROM 19, an abridged map for the entirety of each ofthe routes is generated and displayed upon the display monitor 16.

The current position detection device 14 is an apparatus for detectingthe current position of the vehicle, and it may comprise, for example, avibration gyro 14 a which detects the direction of progression of thevehicle, a vehicle speed sensor 14 b which detects the vehicle speed, aGPS sensor 14 c which detects the GPS signals from GPS satellites, andthe like. Based upon the current position of the vehicle which has beendetected by this current position detection device 14, the navigationapparatus 1 is able to determine the route search start point whensearching for a recommended route.

The image memory 15 temporarily stores image data for display upon thedisplay monitor 16. This image data consists of data for road mapdrawing and various types of diagrammatical data for image display of anabridged map and the like, and is generated by the control circuit 11,based upon the map data which is recorded on the DVD-ROM 19. An abridgedmap of the entirety of each of the various routes is displayed upon thedisplay monitor 16, using this image data stored in the image memory 15.

The input device 17 has various types of input switches for the user toperform setting of the destination and the like, and this may beimplemented as an operation panel or a remote controller or the like. Byactuating the input device 17 according to instructions which aredisplayed upon the display monitor 16, the user can designate the nameof a place or a position upon the map and set it as a destination, andcan cause the navigation apparatus 1 to start searching for a route tothis destination.

The disk drive 18 reads out map data which is to be used for generatingan abridged map from the DVD-ROM 19 which is loaded. It should beunderstood that although herein, by way of example, the explanation isgiven in terms of the use of a DVD-ROM, it would also be acceptable toread out the map data from some other recording media other than aDVD-ROM, such as, for example, a CD-ROM or a hard disk or the like. Inthis map data, there may be included route calculation data which isused for calculating a plurality of routes, route guidance data such asintersection names, road names or the like which is used for guiding thevehicle to the destination according to a recommended route which hasbeen selected by the user, road data which specifies roads, andbackground data or the like which indicates map shapes other than roads,such as shorelines, rivers, railroads, various types of facilities(landmarks) upon the map, and so on.

In such road data, the minimum unit which indicates a road section istermed a link. In other words, each road is made up from a plurality oflinks which are set for each predetermined road section. It should beunderstood that the lengths of the road sections set by the links aredifferent; the length of a link is not constant. The points which areconnected together by the links are termed nodes, and these nodesinclude respective position information (coordinate information).Furthermore, points which are termed shape interpolation points betweenone node and another may be set within the links. The shapeinterpolation points include respective position information (coordinateinformation), just like the nodes. The shapes of the links, in otherwords the shape of the road, are determined by the position informationof these nodes and shape interpolation points. Corresponding to eachlink described above, a value termed the link cost is set in the routecalculation data for showing the transit time required by the vehicle.

When a destination is set by operation of the user to the input device17 as described above, the flow chart shown in FIG. 2 is executed by thecontrol circuit 11. Due to this, calculation of route from the currentposition, which has been detected by the current position detectiondevice 14 as a route search start point, to the destination which hasbeen set is performed according to a predetermined algorithm based uponthe route calculation data, and a plurality of routes to the destinationare obtained. An abridged map of the entirety of each of the routeswhich have been obtained in this manner is generated based upon the roaddata, and is displayed upon the display monitor 16.

The flow chart of FIG. 2 will now be explained in the following. In astep S100, the destination for route searching is set according to thedestination which has been inputted by the user. In a step S200, aplurality of routes are searched out from the current position of thevehicle, which is the route search point, to the destination which wasset in the step S100. At this time, the route calculation is performedaccording to the predetermined algorithm, based upon the routecalculation data, as described above. It should be understood that thecurrent position of the vehicle is obtained by the current positiondetection device 14 repeatedly at a fixed interval.

Moreover, in the step S200, in order to find a plurality of routes, theroute searching is performed according to various route searchingconditions. For example, route searching may be performed according to aroute searching condition such as toll road priority, normal roadpriority, distance priority, or the like, and, by obtaining the mostsuitable route under each condition, a plurality of routes may be found.Or a plurality of routes may also be searched out by looking for routesother than the most suitable route under a single route searchingcondition. For example, it would be possible to find a plurality ofroutes with a single route searching condition by taking the route forwhich the total of the link costs to the destination is the smallest asthe most suitable route, and by moreover obtaining a route search resultwhich also includes routes for which the difference of the total linkcost with respect to this most suitable route is within a predeterminedvalue.

In a step S300, a shoreline extraction procedure is executed. Here, as apreliminary procedure which is required for executing the shorelinedrawing procedure of the step S800, the shapes of the shorelines whichare within a predetermined range from each route which has been found inthe step S200 are extracted. It should be understood that, according torequirements, this shoreline extraction procedure may be executed, ormay not be executed. Since these procedural details have no directrelationship with the present invention, the detailed explanationthereof will be curtailed.

In a step S400, a link compactification procedure is executed. Here, asa preliminary procedure in order to make it possible to perform properprocessing in the abridged map generation procedure of the step S500, aprocedure is performed of compactifying the links for each route whichhas been found in the step S200. In concrete terms, a procedure ofintegrating together adjacent portions of a plurality of links into asingle link (an adjacent link integration procedure), a procedure ofeliminating minute links (a minute link elimination procedure), and aprocedure of eliminating interpolation points for which the gap to aneighboring point is minute (a minute gap intermediate point eliminationprocedure) are executed for each route. It should be understood that,according to requirements, this link compactification procedure may beexecuted, or may not be executed. Since these procedural details have nodirect relationship with the present invention, the detailed explanationthereof will be curtailed.

In a step S500, an abridged map generation procedure is executed uponeach of the routes which were found in the step S200, and upon whichfurthermore, according to requirements, the link compactificationprocedure of the step S400 was executed. The contents of the processingat this time will be explained hereinafter in detail. By this abridgedmap generation procedure, an abridged map is generated which shows eachof the routes in its entirety, in other words from the current positionto the destination.

In a step S600, a scale changing procedure is executed. Here, aprocedure is performed of partially changing the scale of the abridgedmap which was generated in the step S500. For example, the scale of thesurroundings of the departure point or the destination may be madelarger than that of other portions, so that the surroundings of thedeparture point or the destination are magnified and made more easy tosee. It should be understood that, according to requirements, this scalechanging procedure may be executed, or may not be executed. Since theseprocedural details have no direct relationship with the presentinvention, the detailed explanation thereof will be curtailed.

In a step S700, an overlapped portion drawing procedure is executed.Here, a procedure is performed of, for the abridged map which wasgenerated in the step S500, drawing the portions where two or moreroutes overlap one another in a display format which makes it possibleto distinguish between each of these routes. For example, the routes maybe drawn slightly mutually displaced from one another. It should beunderstood that, according to requirements, this overlapped portiondrawing procedure may be executed, or may not be executed. Since theseprocedural details have no direct relationship with the presentinvention, the detailed explanation thereof will be curtailed.

In a step S800, a shoreline drawing procedure is executed. Here, aprocedure is performed of drawing shorelines within a predeterminedrange from the routes, based upon the shapes of shorelines which wereextracted in the step S300. It should be understood that, according torequirements, this shoreline drawing procedure may be executed, or maynot be executed. Since these procedural details have no directrelationship with the present invention, the detailed explanationthereof will be curtailed.

In a step S900, the abridged map of the routes which was generated inthe step S500, and upon which additionally, according to requirements,the procedures of the steps S600˜S800 have been performed, is displayedupon the display monitor 16. At this time, a departure point mark and adestination mark are displayed upon the departure point and upon thedestination, respectively. After having performed this step S900, theflow chart of FIG. 2 terminates. By doing as has been explained above, aplurality of routes to the destination are searched out and an abridgedmap of each of these routes is displayed upon the display monitor 16.

Having executed the procedures of the flow chart of FIG. 2 and displayedan abridged map of the entirety of each of the routes upon the displaymonitor 16, thereafter the navigation apparatus 1 instructs the user toselect one from among the routes. When any one of the routes is selectedby the user actuating the input device 17, the selected route is set asthe recommended route, and is displayed upon the road map of thesurroundings of the current position with an indication that it is therecommended route. And the vehicle is directed according to thisrecommended route, and is guided to the destination. It should beunderstood that at this time, as a road map of the surroundings of thecurrent position, either a normal map or an abridged map may bedisplayed. At this time, an abridged map may be generated by the sameprocedure as that of the flow chart of FIG. 2.

FIG. 3A and FIG. 3B are figures showing a normal map before abridgement,and an abridged map which has been displayed by executing the proceduresof the flow chart of FIG. 2. In the map before abridgement shown in FIG.3A, three routes 63, 64, and 65 which connect from the current position61 to the destination 62 are shown. The abridged map of FIG. 3B isdisplayed by executing the procedures of the flow chart of FIG. 2 uponthese routes 63˜65. It will be understood that, in this abridged map,the road shape of each of the routes 63˜65 is simplified. After havingdisplayed the abridged map of each of the routes by doing this,whichever one of the routes has been selected is taken as therecommended route, and the vehicle is guided from the current position61 to the destination 62.

Next, the details of the abridged map generation procedure which isexecuted in the step S500 will be explained. In this abridged mapgeneration procedure, an abridged map of each of the routes is generatedby simplifying the road shape of each of the routes by executing aprocedure which is termed a direction quantization procedure. Thisdirection quantization procedure will now be explained in the following.

In this direction quantization procedure, simplification of the roadshapes is performed by dividing the links of each route into respectivepredetermined numbers of sections. Each of FIGS. 4A, 4B, 4C, and 4D, andFIGS. 5A, 5B, 5C, and 5D is a detailed explanatory figure for explainingthe details of this direction quantization procedure: in FIGS. 4A˜4D,the details of the direction quantization procedure are shown for thecase in which the number of link sections is two (division into twosections); while, in FIGS. 5A˜5D, the details of the directionquantization procedure are shown for the case in which the number oflink sections is four (division into four sections). In the following,first, explanation will be provided for the case of division into twosections, shown in FIGS. 4A through 4D.

The reference symbol 30 in FIG. 4A designates, by way of example, one ofthe links included in a route which has been searched out. For this link30, as shown in FIG. 4B, the point 32 upon this link 30 which isfurthest from the line segment 31 which connects together both its endpoints is selected. It should be understood that the point 32 which isselected here corresponds to a previously described shape interpolationpoint, and both of the end points correspond to nodes.

When the point 32 as described above has been obtained, next, linesegments 33 and 34 are established which connect, respectively, the twoend points of the link 30 with the point 32, as shown in FIG. 4C. Theangles respectively formed between these line segments 33 and 34 andreference lines are defined as θ₁ and θ₂ respectively. It should beunderstood that, here, by reference lines are meant lines which extendfrom both the end points of the link 30 in a direction which isdetermined in advance (for example, the true north direction). As shownin FIG. 4C, the angle of the portion which is sandwiched between thereference line from one end point and the line segment 33 is termed θ₁.Moreover, the angle of the portion which is sandwiched between thereference line from the other end point and the line segment 34 istermed θ₂.

After having established the line segments 33 and 34 which connect thepoint 32 and the two end points of the link 30 respectively in the abovedescribed manner, next, as shown in FIG. 4D, the directions of theseline segments 33 and 34 are each quantized. Here, quantization of thesedirections means that each of the line segments 33 and 34 is rotatedaround its end point as a center so that the above described angles θ₁and θ₂ become integer multiples of some unit angle which is set inadvance. In other words, the values of θ₁ and θ₂ are revised by rotatingthe respective line segments 33 and 34, so that θ₁=m·Δθ and θ₂=n·Δθ(where n and m are integers). The values of m and n in the abovedescribed equation are set so that the θ₁ and θ₂ after revision whichare calculated according to this equation are the closest to theirrespective original values.

When the directions of the line segments 33 and 34 are both quantized asexplained above, the angles θ₁ and θ₂ which the line segments 33 and 34make with the reference lines are revised so as to be multiples of theunit angle Δθ. It should be understood that, in FIG. 4D, Δθ=15°. And inthe figure an example is shown in the figure in which, for θ₁, m is setto be equal to 6, so that the angle after revision becomes 90°, while,for θ₂, n is set to be equal to 0, that the angle after revision becomes0°.

After having quantized the directions of both of the line segments 33and 34 in this manner, next, the point of intersection when both of theline segments 33 and 34 are prolonged is obtained. And the lengths ofboth of the line segments 33 and 34 are revised, so as to connect thispoint of intersection with both of the end points, as shown in FIG. 4D.

As has been explained above, the direction quantization procedure forthe case of division of the link 30 into two sections is performed byobtaining the line segments 33 and 34, and by quantizing theirdirections as well as adjusting their lengths. By using these linesegments 33 and 34 instead of the link 30, it is possible to display theshape of the link 30 in a simplified manner. Since, at this time, theshape of the link 30 is simplified in the state in which the positionsof both the endpoints of the link 30 are fixed, thus no influence isexerted upon the positions of the adjacent links.

Accordingly it is possible easily to simplify the shape of a road, withmaintaining the overall positional relationships of the route, bysimplifying each of the link shapes of the route by using this directionquantization procedure.

Next, the case of division into four sections will be explained. In FIG.5A, just as in FIG. 4A, the reference symbol 40 denotes, as an example,one link included in a route which has been searched out. First, asshown in FIG. 5B, the point 42 a upon the link 40 which is furthest fromthe line segment 41 a which joins together both the end points of thislink 40 is selected. Next, the two line segments 41 b and 41 c whichconnect together this point 42 a and the two end points of the link 40are established, and the points 42 b and 42 c upon the link 40 which arerespectively positioned furthest away from these line segments 41 b and41 c are selected. It should be understood that the points 42 a through42 c which are selected here all correspond to the previously describednodes or shape interpolation points, just as in the case of divisioninto two sections.

After having obtained the points 42 a through 42 c as described above,next, as shown in FIG. 5C, just as in the case of division into twosections, the line segments 43, 44, 45, and 46 are established whichconnect together the end points of the link 40 and the points 42 athrough 42 c, in the irrespective order. The angles respectively formedbetween these line segments 43 through 46 and reference lines areexpressed as θ₃, θ₄, θ₅, and θ₆ respectively. It should be understoodthat the reference lines at this time are not only determined at boththe endpoints of the link 40, but rather are also determined at thepoint 42 a which was initially selected, and which is positioned at thecenter of the points 42 a through 42 c.

After having established the line segments 43 through 46 as describedabove, next, as shown in FIG. 5D, the direction of each of these linesegments is quantized. At this time, taking the point 42 a as apreserved point, the line segments 44 and 45 are each rotated about thispreserved point 42 a as a center. It should be understood that, for theline segments 43 and 46, they are each rotated about the end points as acenter, in the same manner as in the case of division into two sections.Here an example is shown in which Δθ=15° is set in advance, and, afterrevision, the angles θ₃, θ₄, θ₅, and θ₆ have become, respectively, 60°,45°, 180°, and 60°.

After having quantized the directions of each of the line segments 43through 46 in this manner, next, the points of intersection are obtainedwhen the line segments 43 and 44 have both been prolonged, and when theline segments 45 and 46 have both been prolonged. And, as shown in FIG.5D, the lengths of the line segments 43 through 46 are each revised, sothat each of the points of intersection is connected with each of theend points or the preserved point 42 a.

As has been explained above, the direction quantization procedure fordivision of the link 30 into four sections is performed by obtaining theline segments 43 through 46, and by quantizing their directions as wellas adjusting their lengths. By using these line segments 43 through 46instead of the link 40, it is possible to display the shape of the link40 in a simplified manner. At this time, the shape of the link 40 issimplified in the state in which, in addition to the positions of boththe end points of the link 40, also the position of the preserved point42 a is also fixed. Accordingly, even for a route which is made up fromlinks of a complicated shape, it is possible to simplify the shape of aroad appropriately while maintaining its overall positionalrelationships.

It should be understood that although, in the above, the directionquantization procedure has been explained for the cases of division intotwo sections and division into four sections, it would also be possibleto perform this direction quantization procedure in the same manner fordivision into any other number of sections. For example, in a case ofdivision into eight sections, first, just as in the case of divisioninto four sections, the furthest point from the line segment whichconnects together both end points of the link, and the furthest twopoints from each of the two line segments which connect together thatpoint and the two endpoints, are selected. After this, further, thefurthest four points from each of the four line segments which connectbetween these three points with the addition of both the endpoints areselected. By doing this, eight line segments are obtained which connectin order between the total of seven points and the two end points whichhave been selected, and it is possible to perform the directionquantization procedure of division into eight portions by performingquantization of the directions and adjustment of the lengths of theseline segments, in the manner previously described.

How many sections should be employed for the direction quantizationprocedure may be set in advance, or may also be decided according to theshapes of the links. For example when, as described above, proceeding toselect in order the furthest point from each line segment which joinsbetween both endpoints or the points which have been selected up tillthis time—in other words, when repeating the procedure explained inFIGS. 4B and 5B—then the procedure may be repeated until the distancefrom each of the line segments to the furthest point becomes less than apredetermined value, and a number of points may be selected in ordercorresponding to the number of times that procedure was performed. Ifthis is done, it is possible to determine upon the number of sectionsfor the direction quantization procedure according to the shapes of thelinks.

In the direction quantization procedure of division into two sectionswhich was explained with reference to FIGS. 4A through 4D, it may happenthat there is no appropriate point of intersection, even though both ofthe line segments 33 and 34 after their directions have been quantizedare prolonged. In other words, if the line segments 33 and 34 becomeparallel to one another after their directions have been quantized, itmay happen that no point of intersection exists, since when these linessegments are prolonged, they both combine together to become a singleline segment which connects together both of the end points of the link33. In this type of case, the shape of the link 30 may be shown assimplified by using the line segment which directly connects togetherboth of its end points, in other words by using the line segment 31.Furthermore, in the direction quantization procedure of division intofour sections which was explained with reference to FIGS. 5A through 5D,or in a direction quantization procedure of division into more sectionsthan four, in the same manner, if no appropriate point of intersectionexists when the line segments are prolonged after quantizing theirdirections, then it will be acceptable to perform a directionquantization procedure with a smaller number of sections.

It is possible to generate an abridged map by simplifying the road shapeof each route by performing a direction quantization procedure as hasbeen explained above upon all of the links of each route in order. Itshould be understood that it would also be acceptable to execute thedirection quantization procedure as described above, not by units oflinks, but rather for each link series which is made up by lining up aplurality of links. In this case not only shape interpolation points,but also nodes, come to be included in the points which are selected asthe point 32 of FIG. 4B or as the points 42 a through 42 c of FIG. 5B.

Or, in the abridged map generation procedure of the step S500, it isalso possible to simplify the road shape of each route, withoutexecuting the above described direction quantization procedure. In thisconnection, a method of simplifying the road shapes of the routes byapproximating the shape of each link with a curve will now be explainedwith reference to FIGS. 6A, 6B, and 6C.

In FIG. 6A, by way of example, links 50, 51, and 52 are shown as onepart of the links included in a route which has been found. For theselinks 50 through 52, first, as shown in FIG. 6B, the link directionsquantized at both end points of each link are obtained. Here, in thesame manner as when performing quantization of the directions of eachline segment in the previously described quantization procedure, thelink direction is obtained which is the integral multiple of a unitangle closest to the original angle. As a result, link directions ateach end point are obtained as shown by the arrow signs in FIG. 6B.

Next, as shown in FIG. 6C, the shape of each of the links isapproximated by a curve, by obtaining curves 53, 54, and 55 whichconnect between its end points. At this time, the shape of each of thecurves 53 through 55 is determined so that the direction of the tangentline in the vicinity of the end points of each curve agrees with theabove described quantized link direction. It should be understood thatalthough, as methods for obtaining this type of curve, splineapproximation or the like using, for example, spline functions areavailable, the detailed explanation thereof will herein be omitted.

It is possible to generate an abridged map in which the road shape ofeach route is simplified by proceeding with the execution of procedureslike those explained above for all the links of each route in order, andby displaying the road shapes using the curves which have been obtained.At this time as well, the shape of each link is simplified in a state inwhich the positions of both of the end points of that link are fixed, inthe same way as in the case of the direction quantization procedure.Accordingly, in this case as well, it is possible to simplify the roadshape of each route in a simple manner, while maintaining its overallpositional relationships.

According to the embodiment explained above, the following operationalbenefits are obtained.

-   (1) Since it is arranged to simplify the shape of each link or link    series with the positions of both the end points of the link or link    series being fixed, accordingly it is possible to simplify the shape    of each link or link series without exerting any influence upon the    positions of the adjacent links or link series. Since as a result it    is possible to simplify the road shapes in a simple manner while    maintaining overall positional relationship of the roads,    accordingly it does not happen that the position of the roads    deviate to a large extent from their original position, even when    simplifying the road shapes over a long distance.-   (2) In the direction quantization procedure when dividing into four    sections, it is arranged to simplify the shapes of the links or the    link series in the state in which, in addition to the positions of    both of their end points, the position of the preserved point 42 a    is also kept fixed. Since this is done, it is possible to simplify    the road shapes in an appropriate manner, even for roads which are    built up from links or link series of complicated shapes.    Furthermore since, at this time, it is arranged to select, as the    preserved point, the point 42 a which is the furthest from the line    segment 41 a which connects between both of the end points,    accordingly it is possible to simplify the shapes of the links or    the link series by selecting an appropriate preserved point in a    simple manner.-   (3) By arranging to simplify the shapes of the links or the link    series using a direction quantization procedure, it is possible to    simplify the shapes of the links or the link series by a simple    procedure.-   (4) In the direction quantization procedure when dividing into two    sections, it is arranged to perform the direction quantization    procedure by selecting the point 32 which is the furthest from the    line segment 31 which connects between both of the end points.    Furthermore, in the direction quantization procedure when dividing    into four sections, it is arranged to perform the direction    quantization procedure by selecting the point 42 a which is the    furthest from the line segment 41 a which connects together the two    end points, and furthermore by selecting the points 42 b and 42 c    which are the furthest from the line segments 41 b and 41 c which    connect between this point 42 a and each of the end points,    respectively. Since this is done, it is possible to select    appropriate points in a simple manner when performing the direction    quantization procedure and simplify the shapes of the links or link    series.

Although, in the above described embodiment, the explanation is made interms of an example in which the map data is read out from a storagemedia such as a DVD-ROM or the like by the navigation apparatus, and anabridged map is generated, the present invention is not limited by thesedetails. For example, it would also be possible to apply the presentinvention to a communicating navigation apparatus or the like whichdownloads the map data from an information distribution center, usingwireless communication with a portable telephone or the like. In thiscase, the procedure of generating an abridged map as explained above maybe performed by the information distribution center, with the resultthereof being outputted from the information distribution center as asignal which is distributed to the navigation apparatus. In other words,the information distribution center consists of an apparatus whichgenerates the abridged map, and an apparatus which outputs this abridgedmap to the outside as a signal.

FIG. 7 is a figure illustrating this situation. A communication terminal300 is connected to a navigation apparatus 200 which is fitted to avehicle 100. A portable telephone or the like is used in thiscommunication terminal 300. The communication terminal 300 is connectedwirelessly to a mobile communication network 400. An informationdistribution center 500 is connected to the mobile communication network400. In other words, the navigation apparatus 200 is connected to theinformation distribution center 500 via the communication terminal 300and the mobile communication network 400. When the navigation apparatus200 is connected to the information distribution center 500, ittransmits a distribution request for the map data to the informationdistribution center 500. According to this distribution request, theinformation distribution center 500 performs the procedures detailedabove, and distributes the map data to the navigation apparatus 200. Thenavigation apparatus 200 receives the map data which has beendistributed from the information distribution center 500 via the mobilecommunication network 300 and the communication terminal 200. Thepresent invention may be applied to this type of communicatingnavigation system as well.

It should be understood that, if the present invention is applied to apersonal computer or the like, then it is possible to provide a programrelated to the above described type of control via a recording mediumsuch as a CD-ROM or the like, or via an electrical communication channelsuch as the Internet or the like. FIG. 8 is a figure illustrating thissituation. A personal computer 600 receives supply of a program via aCD-ROM 602. Furthermore, the personal computer 600 is endowed with afunction of connection to a communication channel 601, so that the abovedescribed program may be supplied from a server 603. The communicationchannel 601 is a communication channel such as the internet, a personalcomputer link or the like, or is a dedicated communication channel orthe like. The server 603 transmits the program via the communicationchannel 601 to the personal computer 600. In other words, it convertsthe program to a data signal upon a carrier wave, and transmits it viathe communication channel 601. In this manner, the program may besupplied, in the form of a computer program product which can be read inby a computer, in various formats, such as a recording medium or acarrier wave or the like.

The present invention is not limited to the above described embodiments.Other modes which may be conceived of within the range of the technicalconcept of the present invention are also included within the range ofthe present invention.

1. An abridged map generating apparatus, comprising: an abridged mapgeneration unit that generates an abridged map in which a shape of aroad is simplified based upon road map data that specifies the shape ofthe road by shapes of links set for each predetermined road section, bysimplifying a share of a link or link series with fixed positions ofboth end points of the link or link series made by lining up a pluralityof the links; a point selection unit that selects some point set inadvance upon the link; a line segment setting unit that sets a pluralityof second line segments which connect between the point selected by thepoint selection unit and each of both the end points in order; adirection revision unit that revises directions of each of the secondline segments set by the line segment setting unit, so that each anglewhich is formed between each of the second line segments and apredetermined direction set in advance becomes an integer multiple of anunit angle set in advance; an intersection point detection unit thatobtains a point of intersection on which respective prolonged linesegments obtained by prolonging the second line segments of which thedirection has been revised by the direction revision unit areintersected each other; and a length revision unit that revises a lengthof each of the second line segments, so as to connect together the pointof intersection obtained by the intersection point detection unit andone of the end points or one of the points selected by the pointselection unit; and wherein: the abridged map generation unit generatesthe abridged map by simplifying the shape of the link or link series, byusing each of the second line segments of which the length are revisedby the length revision unit.
 2. An abridged map generating apparatusaccording to claim 1, wherein: when the abridged map generation unitsimplifies the shape of the link or link series, any point set inadvance upon the link is selected as a preserved point and a position ofthe preserved point and the positions of both the end points are fixedrespectively.
 3. An abridged map generating apparatus according to claim2, wherein: the abridged map generation unit selects a point as thepreserved point which is furthest from a first line segment whichconnects between both the end points among points set in advance uponthe link.
 4. An abridged map generating apparatus according to claim 3,wherein: the point selection unit selects the point which is furthestfrom a first line segment which connects between both the end pointsamong points set in advance upon the link.
 5. An abridged map generatingapparatus according to claim 4 wherein: the point selection unit furtherselects points which are furthest respectively from the second linesegments set by the line segment setting unit among points set inadvance upon the link; the line segment setting unit further sets aplurality of second line segments which connect between each of thepoints further selected by the point selection unit and each of the endpoints and the points previously selected by the point selection unit inorder; and the point selection unit and the line segment setting unitrepeat the selection of points and the setting of second line segmentsrespectively.
 6. An abridged map generating apparatus according to claim2, wherein: the point selection unit selects the point which is furthestfrom a first line segment which connects between both the end pointsamong points set in advance upon the link.
 7. An abridged map generatingapparatus according to claim 6, wherein: the point selection unitfurther selects points which are furthest respectively from the secondline segments set by the line segment setting unit among points set inadvance upon the link; the line segment setting unit further sets aplurality of second line segments which connect between each of thepoints further selected by the point selection unit and each of the endpoints and the points previously selected by the point selection unit inorder; and the point selection unit and the line segment setting unitrepeat the selection of points and the setting of second line segmentsrespectively.
 8. An abridged map generating apparatus according to claim1, wherein: the point selection unit selects the point which is furthestfrom a first line segment which connects between both the end pointsamong points set in advance upon the link.
 9. An abridged map generatingapparatus according to claim 8, wherein: the point selection unitfurther selects points which are furthest respectively from the secondline segments set by the line segment setting unit among points set inadvance upon the link; the line segment setting unit further sets aplurality of second line segments which connect between each of thepoints further selected by the point selection unit and each of the endpoints and the points previously selected by the point selection unit inorder; and the point selection unit and the line segment setting unitrepeat the selection of points and the setting of second line segmentsrespectively.
 10. An on-vehicle information terminal, comprising: anabridged map generating apparatus according to claim 1; and a displaycontrol unit that causes an abridged map generated by the abridged mapgenerating apparatus to be displayed upon a display monitor.
 11. Anabridged map distribution system, comprising: an abridged map generatingapparatus according to claim 1; a distribution apparatus thatdistributes an abridged map generated by the abridged map generatingapparatus; and a navigation apparatus that receives the abridged mapdistributed by the distribution apparatus.
 12. An abridged mapgenerating method for generating an abridged map in which a shape of aroad is simplified based upon road map data that specifies the shape ofthe road by shapes of links set for each predetermined road section, bysimplifying a share of a link or link series with fixed positions ofboth end points of the link or link series made by lining up a pluralityof the links, the method comprising: se1ecting some point set in advanceupon the link; setting a plurality of second link segments which connectbetween the selected point and each of both the end points in order;revising directions of each of the second line segments, so that eachangle which is formed between each of the second line segments and apredetermined direction set in advance becomes an integer multiple of anunit angle set in advance; obtaining a point of intersection on whichrespective prolonged line segments obtained by prolonging the secondline segments of which the direction has been revised are intersectedeach other; revising a length of each of the second line segments, so asto connect together the obtained point of intersection and one of theend points or one of the selected points; and generating the abridgedmap by simplifying the shape of the link or link series, by using eachof the second line segments of which the length are revised.